The invention relates to electronic optical apparatus and more particularly to an improvement of this type of apparatus.
In an electron scan microsope or an electron probe X ray analyzer, the sample to be observed or to be analyzed is subjected to bombardment by the electrons of an electron beam, generated by an electron gun then deflected and focussed for scanning the sample.
Over the whole path of the electron beam, the parts situated in the immediate vicinity thereof are struck by primary electrons, and back-scattered parasite electrons disturb the useful beam, causing limitation of the spatial resolution of the apparatus both for observation and X ray analysis. This back-scattering occurs more particularly at the level of the anode of the electron gun and of the protecting tube passing through the condensor block of the beam, as well as at the level of the deflection block in front of the final focussing lens of the beam.
To partially resolve this problem, in some apparatus of this type, screens are disposed, at selected locations, to eliminate these parasite electrons so as to limit the disturbance of the useful beam.
The invention relates to an improved electronic optical apparatus in that the number of parasite electrons disturbing the beam is considerably reduced with respect to that existing in apparatus of this type in which the protecting screens are usually made from metal, for example stainless steel or copper alloys.